Internal combustion engines have long been implemented with various control strategies for skipping a supply of fuel in one or more cylinders of an engine and subsequently, omitting a firing event in cylinders of the engine to which the supply of fuel has been skipped.
For reference, U.S. Pat. No. 5,377,631 (hereinafter referred to as ‘the '631 patent’) relates to strategies for operating a four cycle engine in a skip-cycle manner. The '631 patent discloses providing the engine with a valve control so that each intake and exhaust valve for each cylinder can be individually activated or deactivated essentially instantaneously to provide a skip-cycle pattern that varies as a function of the load. Each of the valves permits changing the purpose of the stroke of each piston of each deactivated cylinder from compression to exhaust or intake to expansion, as the case may be, to assure firing of all of the engine cylinders within as short a period as one skip cycle to prevent cylinder cool-down, which promotes emissions. Un-throttled operation also is provided by closing the intake and exhaust valves in a particular sequence during skip cycle operation, and controlling the intake valve closure timing during load periods between skip cycle periods to continue un-throttled operation for all load levels. Further individual activation or deactivation of the fuel injectors and spark plugs enhances the skip cycle and un-throttled operation.
However, in most cases, it has been observed that a common pattern of skipping the supply of fuel-air mixture, and subsequently omitting the firing in cylinders is to skip the supply of fuel-mixture in a given cylinder for merely one working cycle of the engine at a time and repeating such skip-firing in rest of the cylinders sequentially.
Although skipping a supply of fuel and subsequent combustion in a given cylinder for merely one cycle at a time may be advantageous in various operating conditions of the engine, during a start of the engine and/or a low-load condition of the engine, a quick alternation of skip-firing from one cylinder to the next may result in a majority of the cylinders having an average temperature of the engine. However, for a large number of cylinders in a given engine, this temperature of the skipped cylinders may still be too cold for having a complete combustion of the fuel-air mixture in the cylinders of the engine.
Hence, there is a need for control strategies that enable a more effective skip-firing pattern while also maintaining optimum performance by internal combustion engines during start and low-load conditions.